Patent Application
20210184254
Rechargeable lithium-ion batteries (LIBs) are widely used in various portable electronics since their first commercialization by Sony Corporation in 1991. Now LiCoO2 (LCO) is used presently in >31% of LIBs that are manufactured. Specifically, the LCO has a high theoretical capacity of 274 mAh g−1, but the practical discharge capacity is only ˜145 mAh g−1 (Li1-xCoO2, x˜0.5, ˜4.25 V vs. Li/Li+). When operating at voltages >4.25 V to get a higher capacity, the cycling efficiency and discharge capacity of LCO cells decay rapidly. And the electrolytes using in LIBs are flammable, which have potentially thermal runaway and catastrophic failures in large-scale deployment.
LIBs with higher energy density and greater power output are urgently needed. To realize high energy density, significant developments of cathode materials (e.g., high-voltage LiCoO2 (LCO), Ni-enriched Li(NiCoyMn1−x−y)O2(NCM) and LiNi1−x−yCoxAlyO2 (NCA)) with either high capacity or high voltage, as well as anodes with high capacity (e.g. lithium metal) should be used. Along with the pursuit of high energy density, safety is also critical component to avoid thermal runaway and catastrophic failures in large-scale deployment. To become viable, the cathode materials should be useable at higher voltages and the electrolytes for lithium batteries should have high flash point, which is difficult to ignite.
Solid electrolytes include both ceramic electrolytes and polymer electrolytes. Although ceramic electrolytes have high conductivities of 10−4-10−2 S/cm, their usage is still impeded by the high interfacial impedance with electrode materials. Furthermore, it is also a great challenge to manufacture pure ceramic-based solid state batteries at large scale.
Polymer electrolytes, such as poly (ethylene oxide) (PEO), have gained widespread interest as promising candidates for rechargeable solid-state lithium batteries because of their low cost and compatibility with state-of-the-art manufacturing processes. PEO-based electrolytes are much safer than liquid electrolytes due to the high flash point. PEO electrolytes have been reported to be chemically compatible with lithium metal, which makes them more attractive than carbonate electrolytes used in Li-ion batteries. Electric vehicle “Bluecars” equipped with LiFePO4 (LFP)/PEO/Li-metal battery have been commercialized by Bollore. However, they need to be operated at 70-80° C. and has a limited specific energy of 100 Wh kg−1 at the system level. Further, the poor interfacial stability between the high voltage cathodes, such as LCO and NCM, limits their viability, and PEO electrolytes further impede their applications in 4 V lithium batteries with high energy density, which substantially deteriorates the cycling performance and significantly limits the energy density. Additionally, the unsatisfactory ionic conductivity, <10−4 S/cm at room temperature, hinders their practical applications in high-performance batteries.
Some embodiments of the present disclosure are directed to a cathode for use in a lithium-ion battery, including a substrate and a coating disposed on the substrate including one or more layers, the coating configured to stabilize an interface between the substrate and a polymer electrolyte. In some embodiments, the substrate includes LiCoO2 (LCO), Li(NixCoyMn1−x−y)O2 (NCM), LiNi1−x−yCoxAlyO2 (NCA), or combinations thereof. In some embodiments, the one or more layers includes a metal oxide. In some embodiments, the metal oxide is aluminum oxide. In some embodiments, the metal oxide layer has thickness between about 1 nm and about 3 nm. In some embodiments, the one or more layers includes a ceramic electrolyte. In some embodiments, the ceramic electrolyte includes Li1.5Al0.5Ge1.5(PO4)3(LAGP), Li1+xAlxTi2−x(PO4)3 (LATP), or combinations thereof. In some embodiments, the cathode has a weight percent of ceramic electrolyte between about 0.5% and about 10%. In some embodiments, the cathode has a weight percent of ceramic electrolyte between about 1.5% to about 3.5%. In some embodiments, the one or more layers includes a decomposed salt layer.
Some embodiments of the present disclosure are directed to a lithium-ion battery, including a cathode including a substrate and a coating disposed on the substrate, an anode, and an electrolyte interfacing with both the cathode and the anode, wherein the coating includes one or more layers and is configured to stabilize an interface between the cathode and the electrolyte, wherein the one or more layers includes an oxide or a ceramic compound, and wherein the battery is configured for stabile operation at or above 4 V. In some embodiments, the electrolyte includes poly(ethylene oxide) (PEO), polyethylene glycol (PEG), a carbonate, or combinations thereof, and one or more salts including lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium hexafluorophosphate (LiPF6), Li7La3Zr2O12 (LLZO), aluminum oxide, or combinations thereof. In some embodiments, the substrate includes LiCoO2 (LCO), Li(NixCoyMn1−x−y)O2 (NCM), LiNi1−x−yCoxAlyO2 (NCA), or combinations thereof, and the coating includes Li1.5Al0.5Ge1.5(PO4)3 (LAGP), Li1+xAlxTi2−x(PO4)3 (LATP), aluminum oxide, or combinations thereof. In some embodiments, the anode includes lithium metal or graphite.
Some embodiments of the present disclosure are directed to a method of making a cathode for use in a lithium-ion battery, the method including grinding one or more substrate materials and one or more ceramic electrolytes, combining the one or more substrate materials and the one or more ceramic electrolytes with a solvent to form a composite, and sintering the composite. In some embodiments, grinding the one or more substrate materials and ceramic electrolytes includes a ball milling process. In some embodiments, sintering the composite includes drying the composite and sintering the dried composite above about 600° C. In some embodiments, the method includes forming in situ a decomposed salt layer over the composite.
Some embodiments of the systems and methods of the present disclosure are directed to a cathode 100 for use in an energy storage device, e.g., in a lithium-ion battery. In some embodiments, the cathode includes a substrate 102 and a coating 102A disposed on the substrate. In some embodiments, substrate 102 and coating 102A include materials exhibiting high capacity and suitability for operation at high voltage, e.g., above about 4 V. In some embodiments, the substrate includes LiCoO2 (LCO), Li(NixCoyMn1−x−y)O2(NCM), LiNi1−x−yCoxAlyO2 (NCA), or combinations thereof.
In some embodiments, coating 102A includes one or more layers 102′. Coating 102A is configured to stabilize an cathode electrolyte interface 104 between substrate 102 and an electrolyte, e.g., electrolyte E. In some embodiments, one or more layers 102′ include a metal oxide. Without wishing to be bound by theory, the metal oxide layer passivates the surface of cathode 100, a surface of substrate 102, creating the 104 that suppresses oxidation of electrolytes, such as the polymer electrolytes discussed below. The result is advantageously stabilized coulombic efficiency and cycling performance of cathode 100. In some embodiments, the metal oxide includes aluminum oxide. In some embodiments, the metal oxide layer has a thickness of about 1 nm to about 3 nm. In some embodiments, the metal oxide layer has a thickness of about 2 nm. In some embodiments, one or more layers 102′, e.g., the metal oxide, is disposed on cathode 100 via an atomic layer deposition process.
In some embodiments, one or more layers 102′ include a ceramic compound. In some embodiments, one or more layers 102′ include a ceramic electrolyte. Without wishing to be bound by theory, the ceramic electrolyte facilitates ion transport within cathode 100 and prevents oxidation of electrolyte, e.g., electrolyte E, as will be discussed in greater detail below. In some embodiments, the ceramic electrolyte includes Li1.5Al0.5Ge1.5(PO4)3(LAGP), Li1+xAlxTi2-x(PO4)3 (LATP), or combinations thereof. In some embodiments, cathode 100 has a weight percent of ceramic electrolyte between about 0.5% and about 10%. In some embodiments, cathode 100 has a weight percent of ceramic electrolyte between about 0.5% and about 4.5%. In some embodiments, cathode 100 has a weight percent of ceramic electrolyte between about 1.5% to about 3.5%. In some embodiments, the ceramic electrolyte is incorporated into cathode 100 using a ball milling and sintering process, as will be discussed in greater detail below. In some embodiments, one or more layers 102′ include one or more LixPOy layers suitable for use with substrate 102 and a ceramic electrolyte. In some embodiments, one or more layers 102′ include Li3PO4, Li4P2O7, etc., or combinations thereof. In some embodiments, one or more layers 102′ include a separate polymeric coating suitable for use with substrate 102 and a ceramic electrolyte.
In some embodiments, one or more layers 102′ include a decomposed salt layer. In some embodiments, the decomposed salt layer is formed in situ over a ceramic electrolyte layer, as will be discussed in greater detail below.
In some embodiments, electrolyte E includes a carbonate. In some embodiments, electrolyte E includes ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, or combinations thereof. In some embodiments, electrolyte E is a polymer electrolyte. In some embodiments, electrolyte E includes poly(ethylene oxide) (PEO), polyethylene glycol (PEG), or combinations thereof. In some embodiments, electrolyte E includes one or more salts. In some embodiments, the one or more salts include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium hexafluorophosphate (LiPF6), Li7La3Zr2O12 (LLZO), aluminum oxide, or combinations thereof.
Due to the small thickness of coating 102A, the cathode electrolyte interface 104 does not sacrifice energy density significantly while it remarkably enhances cycling performance. By deploying such cathode electrolyte interface strategy, high capacity retentions of 81.9% over 400 cycles and 84.7% over 200 cycles are achieved in LAGP-LCO/PEO/Li cells at 60° C. with charging cut-off of 4.25 V and 4.3 V, respectively. The stability is further validated in harsher conditions, wherein capacity retention of 88.1%/70 cycles when charged to 4.4 V, and 88.5%/150 cycles at RT are observed. This strategy can also be generalized to NCM, and steady cycling of 93.8% over 100 cycles is observed in NCM523/PEO/Li cells.
Referring now to
In some embodiments, anode 204 can be of any material or combination of materials suitable for use with cathode 202 and electrolyte 206. In some embodiments, anode 202 includes lithium metal or graphite. As discussed above, in some embodiments, electrolyte 206 includes a carbonate. In some embodiments, electrolyte 206 includes ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, or combinations thereof. In some embodiments, electrolyte 206 is a polymer electrolyte. In some embodiments, electrolyte 206 includes poly(ethylene oxide) (PEO), polyethylene glycol (PEG), or combinations thereof. Without wishing to be bound by theory, polymer electrolytes such as PEO are much safer than conventional liquid electrolytes due to their high flash point. Difficulties operating these polymer electrolytes at higher voltages have limited their usage in high energy density and power capability applications. However, the coatings according to some embodiments of the present disclosure are able to stabilize the interface of the polymer electrolyte and the cathode, preventing harmful oxidation of the electrolyte and enabling use of the electrolyte in higher voltage applications.
In some embodiments, electrolyte 206 includes one or more salts. In some embodiments, the one or more salts include lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalato)borate (LiBOB), lithium hexafluorophosphate (LiPF6), Li7La3Zr2O12 (LLZO), aluminum oxide, or combinations thereof. In some embodiments, one or more layers 202′ include a decomposed salt layer. Referring now to
In some embodiments, energy storage device 200 is configured for stabile operation at or above 4 V. In some embodiments, energy storage device 200 is configured for stabile operation at or above 4.25 V. In some embodiments, energy storage device 200 is configured for stabile operation at or above 4.5 V.
Referring now to
Referring to
Three different kinds of electrolyte combinations were explored, including LiTFSI/LiBOB/LiPF6 in PEO/PEGDME (electrolyte-1), PEO/PEGDME/EC/PC (electrolyte-2), and PEO/LLZO/PEGDME/EC/PC (electrolyte-3), where LiTFSI, LiBOB, PEGDME, EC, PC, and LLZO are short for lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, polyethylene glycol dimethyl ether (Mw=500), ethylene carbonate, propylene carbonate and Ta-doped Li7La3Zr2O12, respectively. PEO has an Mw of 10,000 in all electrolytes. Electrolyte-1 is used as the baseline, while the other two were explored for enhancing conductivity and polymer/ceramic composite electrolyte, respectively. The exact compositions are illustrated in Table 1.
These electrolytes are all solid-state at RT. The electrolytes are also fire-retardant and show excellent thermal stability, as characterized by resistance to ignition. Electrolyte-1, 2 and 3 show ionic conductivities of 7.8×10−6, 7.7×10−4 and 2.3×10−4 S cm−1 at RT, which further increase to 7.0×10−4, 2.2×10−3 and 1.1×10−3 S cm−1 at 60° C., respectively. These values are 1-3 orders of magnitude higher than pure PEO electrolytes due to the addition of liquid plasticizer and ceramic electrolytes. The electrolytes also show steady cycling in Li/Li symmetric cells. At 0.3 mA cm−2 and 0.3 mAh cm−2, the overpotential of Li/Li cells only increases from 80 to 120 mV over 2000 hours with electrolyte-1. The surface of Li metal remains dense after cycling, suggesting good interfacial stability between the electrolyte and Li metal.
Given the good stability between the multi-component PEO-based electrolytes and lithium anode, LAGP-LCO/Li cells were further tested in the range of 3-4.25/4.3/4.4 V at 60° C. The current rate was 0.3 C for charging with a constant voltage step down to 0.05 C and 0.5 C for discharge (1 C=145 mA g−1), after one formation cycle at 0.1 C. The LAGP-LCO/Li cell with electrolyte-1 showed excellent cycling performance with an initial specific capacity of 131.2 mAh g−1 and 107.4 mAh g−1 after 400 cycles, which represents capacity retention of 81.9% (see
Significantly enhanced stability was also observed when the cut-off voltage increased to 4.3 V and 4.4 V. At 4.3 V, LAGP-LCO/Li cell showed an initial specific capacity of 150.4 mAh g−1 at 0.1 C and 147.0 mAh g−1 at 0.5 C with electrolyte-1, and slightly decreased to 132.4 mAh g−1 over 200 cycles with a capacity retention of 84.7% (see
When further charged to 4.4 V utilizing electrolyte-2, the initial specific capacity reached 169.2 mAh g−1 at 0.1 C and 163.7 mAh g−1 at 0.5 C for LAGP-LCO, which dropped to 162.5 mAh g−1 after 20 cycles, and 141.2 mAh g−1 after 70 cycles, representing a capacity retention of 86.3% (see
Salt composition of electrolyte was also tested. When LAGP-LCO/Li cell was combined with LiBF4/PEO, the capacity decayed (10.8% retention/100 cycles) with an average CE of 96.9% (see
In order to comprehensively evaluate the performance of 4 V PEO solid batteries with such a coating strategy, their performance was tested at various conditions, such as cycling at RT, using thin Li anode (40 μm), replacing LCO with NCM523, and the addition of LLZO ceramic particles. Steady cycling has been observed in all cases, as discussed below.
First, although 60° C. can be an acceptable temperature for electric vehicles, it is beneficial to have battery functional at RT. By addition of 25 wt. % EC/PC plasticizer inside, the ionic conductivity of PEO electrolyte reached 5.1×10−4 S cm−1 at RT (see
While LCO is a model 4 V cathode, NCM is the standard material in electric vehicles. Thus, the coatings according to some embodiments of the present disclosure were further tested in NCM523. As shown in
Prepared LAGP-LCO cathodes were also tested in LAGP-LCO/Li half cells with most common used commercial liquid electrolytes, including electrolyte-4 (1 M LiPF6 in EC/DEC (EC:DEC=1:1, w/w)) and electrolyte-5 (1.2 M LiPF6 in EC/EMC (EC:EMC=3:7, v/v)), as well as home-made electrolyte-6 (0.6 M LiTFSI+0.4 M LiBOB+0.05 M LiPF6 in EC/PC (EC:PC=3:7, v/v)). The cut-off voltage was set at 3-4.5 V and the cells were charged at 0.3 C, followed by constant voltage charge process until the current density reduced to 0.05 C, then discharged at 1 C (1 C=1.37 mA cm−2).
Different weight ratios of LAGP from 10% to 0.5% were investigated. When the ratio of LAGP utilized decreased from 10 wt. % to 1.5 wt. %, the initial specific capacity increases, while the initial specific capacity decreased with the further decrease of LAGP content. Using electrolyte-4 as an example, the specific capacity increased from 163.1 mAh to 194.4 mAh g−1, followed by dropping to 183.9 mAh g−1 at 0.1 C when the dosage of LAGP decreased from 10 wt. % to 1.5 wt. %, and further to 0. The initial specific capacity and capacity retention are summarized in Table 3:
7%
7%
With electrolyte-4, 3.5% LAGP-LCO/Li cell delivered an initial specific capacity of 183.4 mAh g−1 at 0.1 C and 177.7 mAh g−1 at 1 C, then the specific capacity slightly dropped to 156.4 mAh g−1 after 400 cycles with capacity retention of 88.0% (see
Another commercial electrolyte, 1.2 M LiPF6 in EC/EMC (electrolyte-5), was utilized to demonstrate the significant improvement in electrochemical performance with the LAGP modification. Impressively, stable cycling with ultra-high capacity retention of 95.8%/200 cycles was observed. In these results, 1.5 wt. % LAGP endowed the highest initial specific capacity, 194.4 mAh g−1 at 0.1 C and 192.1 mAh g−1 at 1 C, respectively (see
Besides the cycling stability, 3.5% LAGP-LCO also provided better power capability, featuring reversible specific capacity of 183.0, 180.3, 177.6, 174.0, 166.8, 160.9 mAh g−1 at 0.3 C, 0.5 C, 1 C, 2 C, 4 C, and 6 C with electrolyte-4 in 3-4.5 V, respectively. In contrast, bare LCO cell showed specific capacity of 182.6, 177.8, 171.2, 158.8, 132.6, 108.7 mAh g−1 at 0.3 C, 0.5 C, 1 C, 2 C, 4 C, and 6 C, respectively. The reversible specific capacity of bare LCO was much lower than that of LAGP-LCO at high rates, which can be also observed with electrolyte-6. These results indicate the electrochemical performance is significantly improved with LAGP ceramic electrolyte.
Referring now to
Methods and systems of the present disclosure are advantageous in that they significantly enhance the interfacial stability between cathode and electrolyte in energy storage devices without sacrificing energy density noticeably. The LAGP-LCO cathodes provide good power capability at 60° C., featuring reversible specific capacity of 140.6, 138.5, 134.6, and 118.3 mAh g−1 at 0.1 C, 0.3 C, and 0.5 C, and 1 C in 3-4.25 V, respectively. In contrast, bare LCO cells show specific capacity of 143.1, 136.7, 128.4, and 95.7 mAh g−1 at 0.1 C, 0.3 C, 0.5 C, and 1 C, respectively, lower than that of LAGP-LCO at high rates. Finally, the batteries according to some embodiments of the present disclosure allow for practical use of PEO-based electrolytes, which do not catch fire when ignited. The batteries of the present disclosure also exhibit improved stability between PEO electrolytes and high voltage cathodes, opening up new possibilities for practical application of solid-state lithium metal batteries with high energy density.
Although the invention has been described and illustrated with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without parting from the spirit and scope of the present invention.
This application is a continuation of International Patent Application No. PCT/US2019/049318, filed on Sep. 3, 2019, which claimed the benefit of U.S. Provisional Patent Application Nos. 62/725,914, filed on Aug. 31, 2018; 62/819,224, filed on Mar. 15, 2019; 62/892,226, filed Aug. 27, 2019; 62/893,945, filed Aug. 30, 2019; and 62/893,981, filed Aug. 30, 2019, which are all incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 62725914 | Aug 2018 | US | |
| 62819224 | Mar 2019 | US | |
| 62892226 | Aug 2019 | US | |
| 62893945 | Aug 2019 | US | |
| 62893981 | Aug 2019 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/US2019/049318 | Sep 2019 | US |
| Child | 17186067 | US |
